HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Loo, D. D. F. Articles by Wright, E. M. Search for Related Content PubMed PubMed Citation Articles by Loo, D. D. F. Articles by Wright, E. M.

Passive water and ion transport by cotransporters

Donald D. F. Loo, Bruce A. Hirayama, Anne-Kristine Meinild, Grischa Chandy *, Thomas Zeuthen ¹ and Ernest M. Wright.

The rabbit Na⁺-glucose (SGLT1) and the human Na⁺-Cl^--GABA (GAT1) cotransporters were expressed in Xenopus laevis oocytes, and passive Na⁺ and water transport were studied using electrical and optical techniques. Passive water permeabilities (L_p) of the cotransporters were determined from the changes in oocyte volume in response to osmotic gradients. The specific SGLT1 and GAT1 L_p values were obtained by measuring L_p in the presence and absence of blockers (phlorizin and SKF89976A). In the presence of the blockers, the L_p values of oocytes expressing SGLT1 and GAT1 were indistinguishable from the L_p of control oocytes. Passive Na⁺ transport (Na⁺ leak) was obtained from the blocker-sensitive Na⁺ currents in the absence of substrates (glucose and GABA).

Passive Na⁺ and water transport through SGLT1 were blocked by phlorizin with the same sensitivity (inhibitory constant (K_i), 3-5 µM). When Na⁺ was replaced with Li⁺, phlorizin also inhibited Li⁺ and water transport, but with a lower affinity (K_i, 100 µM). When Na⁺ was replaced by choline, which is not transported, the SGLT1 L_p was indistinguishable from that in Na⁺ or Li⁺, but in this case water transport was less sensitive to phlorizin.

The activation energies (E_a) for passive Na⁺ and water transport through SGLT1 were 21 and 5 kcal mol^-1, respectively. The high E_a for Na⁺ transport is comparable to that of Na⁺-glucose cotransport and indicates that the process is dependent on conformational changes of the protein, while the low E_a for water transport is similar to that of water channels (aquaporins).

GAT1 also behaved as an SKF89976A-sensitive water channel. We did not observe passive Na⁺ transport through GAT1.

We conclude that passive water and Na⁺ transport through cotransporters depend on different mechanisms: Na⁺ transport occurs by a saturable uniport mechanism, and water permeation is through a low conductance water channel. In the case of SGLT1, we suggest that both the water channel and water cotransport could contribute to isotonic fluid transport across the intestinal brush border membrane.

This article has been cited by other articles:

				J. Ashmore Cochlear Outer Hair Cell Motility Physiol Rev, January 1, 2008; 88(1): 173 - 210. [Abstract] [Full Text] [PDF]

				D. D.F. Loo, B. A. Hirayama, M. H. Karakossian, A.-K. Meinild, and E. M. Wright Conformational Dynamics of hSGLT1 during Na+/Glucose Cotransport J. Gen. Physiol., December 1, 2006; 128(6): 701 - 720. [Abstract] [Full Text] [PDF]

				F. M. Charron, M. G. Blanchard, and J.-Y. Lapointe Intracellular Hypertonicity Is Responsible for Water Flux Associated with Na+/Glucose Cotransport Biophys. J., May 15, 2006; 90(10): 3546 - 3554. [Abstract] [Full Text] [PDF]

				T. Zeuthen*, B. Belhage, and E. Zeuthen Water transport by Na+-coupled cotransporters of glucose (SGLT1) and of iodide (NIS). The dependence of substrate size studied at high resolution J. Physiol., February 1, 2006; 570(3): 485 - 499. [Abstract] [Full Text] [PDF]

				J.P. Barfield, C.H. Yeung, and T.G. Cooper The Effects of Putative K+ Channel Blockers on Volume Regulation of Murine Spermatozoa Biol Reprod, May 1, 2005; 72(5): 1275 - 1281. [Abstract] [Full Text] [PDF]

				F. Bourgeois, M. J Coady, and J.-Y. Lapointe Determination of transport stoichiometry for two cation-coupled myo-inositol cotransporters: SMIT2 and HMIT J. Physiol., March 1, 2005; 563(2): 333 - 343. [Abstract] [Full Text] [PDF]

				D. D.F. Loo, B. A. Hirayama, A. Cha, F. Bezanilla, and E. M. Wright Perturbation Analysis of the Voltage-sensitive Conformational Changes of the Na+/Glucose Cotransporter J. Gen. Physiol., December 28, 2004; 125(1): 13 - 36. [Abstract] [Full Text] [PDF]

				E. M. Wright, D. D. F. Loo, B. A. Hirayama, and E. Turk Surprising Versatility of Na+-Glucose Cotransporters: SLC5 Physiology, December 1, 2004; 19(6): 370 - 376. [Abstract] [Full Text] [PDF]

				K. Edashige, Y. Yamaji, F.W. Kleinhans, and M. Kasai Artificial Expression of Aquaporin-3 Improves the Survival of Mouse Oocytes after Cryopreservation Biol Reprod, January 1, 2003; 68(1): 87 - 94. [Abstract] [Full Text] [PDF]

				A. I. Masyuk, T. V. Masyuk, P. S. Tietz, P. L. Splinter, and N. F. LaRusso Intrahepatic bile ducts transport water in response to absorbed glucose Am J Physiol Cell Physiol, September 1, 2002; 283(3): C785 - C791. [Abstract] [Full Text] [PDF]

				S. G. Schultz Epithelial water absorption: Osmosis or cotransport? PNAS, March 27, 2001; 98(7): 3628 - 3630. [Full Text] [PDF]

				P.-P. Duquette, P. Bissonnette, and J.-Y. Lapointe Local osmotic gradients drive the water flux associated with Na+/glucose cotransport PNAS, March 27, 2001; 98(7): 3796 - 3801. [Abstract] [Full Text] [PDF]

				E. M. Wright Renal Na+-glucose cotransporters Am J Physiol Renal Physiol, January 1, 2001; 280(1): F10 - F18. [Abstract] [Full Text] [PDF]

				A.-K. Meinild, D. D. F. Loo, A. M. Pajor, T. Zeuthen, and E. M. Wright Water transport by the renal Na+-dicarboxylate cotransporter Am J Physiol Renal Physiol, May 1, 2000; 278(5): F777 - F783. [Abstract] [Full Text] [PDF]

				P. AGRE Aquaporin Water Channels in Kidney J. Am. Soc. Nephrol., April 1, 2000; 11(4): 764 - 777. [Full Text] [PDF]

				A. S. Verkman and A. K. Mitra Structure and function of aquaporin water channels Am J Physiol Renal Physiol, January 1, 2000; 278(1): F13 - F28. [Abstract] [Full Text] [PDF]

				M. Quick, D. D. F. Loo, and E. M. Wright Neutralization of a Conserved Amino Acid Residue in the Human Na+/Glucose Transporter (hSGLT1) Generates a Glucose-gated H+ Channel J. Biol. Chem., January 12, 2001; 276(3): 1728 - 1734. [Abstract] [Full Text] [PDF]

				D. D. F. Loo, S. Eskandari, K. J. Boorer, H. K. Sarkar, and E. M. Wright Role of Cl- in Electrogenic Na+-coupled Cotransporters GAT1 and SGLT1 J. Biol. Chem., November 22, 2000; 275(48): 37414 - 37422. [Abstract] [Full Text] [PDF]

				S. M. Saparov, D. Kozono, U. Rothe, P. Agre, and P. Pohl Water and Ion Permeation of Aquaporin-1 in Planar Lipid Bilayers. MAJOR DIFFERENCES IN STRUCTURAL DETERMINANTS AND STOICHIOMETRY J. Biol. Chem., August 17, 2001; 276(34): 31515 - 31520. [Abstract] [Full Text] [PDF]

				M. Quick and B. R. Stevens Amino Acid Transporter CAATCH1 Is Also an Amino Acid-gated Cation Channel J. Biol. Chem., August 31, 2001; 276(36): 33413 - 33418. [Abstract] [Full Text] [PDF]

				D. H. Feldman, W. R. Harvey, and B. R. Stevens A Novel Electrogenic Amino Acid Transporter Is Activated by K+ or Na+, Is Alkaline pH-dependent, and Is Cl--independent J. Biol. Chem., August 4, 2000; 275(32): 24518 - 24526. [Abstract] [Full Text] [PDF]